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What is the function and significance of the derailleur on a bike?

Currently, the demand for bicycles is increasing, so manufacturers have improved bicycles by installing bicycle derailleurs. So, do you know what a bicycle derailleur is? What advantages does this part bring? Please refer to the article below for more details!

1. What is a bicycle derailleur?

A bicycle derailleur is a dynamic transmission system commonly found on various types of bicycles including sports bikes, mountain bikes, children’s bikes, derailleur bikes, and geared bikes. This component allows riders to effortlessly adjust the pedaling force, making it easier to navigate different types of terrain.

The bicycle derailleur consists of the following primary components:

1.1. Starter handle

In the first place, the bicycle derailleur will be attached directly to the handlebars, enabling the user to operate and control it.

Bicycle brake levers consist of a left brake lever and a right brake lever. Each hand side has a different function. The left brake lever controls the left derailleur, which shifts the chain between cogs on the bike, while the right brake lever controls the right derailleur, responsible for shifting the chain between cogs.

Starter handleStarter handle
Bike handlebars

1.2. starter thread

The derailleur is commonly referred to as the “brain” of the bicycle derailleur system because it is responsible for transmitting the power necessary for gear shifting. This component ensures that the force from the shift lever is directed to the front and rear derailleurs based on the user’s instructions.

starter threadstarter thread
starter thread

1.3. Subject before and after

The last component of the bicycle derailleur consists of the front and rear derailleurs.

In the previous discussion, it was mentioned that when the left starter pulls the chain up or drops it, the brake lever reacts accordingly by gently pushing the chain up or down.

The upcoming topic covers the rear derailleur, which is responsible for precisely shifting the chains between the various gears and maintaining a consistent cadence. Additionally, the rear derailleur features multiple screws that are utilized to adjust the limits of the smallest and largest cassette, thereby preventing any chain slippage.

2. Principle of operation

Bicycle derailleurs are commonly referred to as speed derailleurs. The left lever is known as a plate shifter. This particular set is equipped with 3 gears, which are crucial in determining cycling speed, as outlined below:

  • Disc n°1 (small disc): used to move on steep terrain, gently pedaling the bicycle to move smoothly.
  • Disc n°2 (medium disc): used on street bikes, vehicles traveling at a moderate speed, neither too fast nor too slow.
  • Disc number 3 (large disc): used for speed enthusiasts wishing to go fast or when practicing a sport.
Bike discsBike discs
Bike discs

The lever situated on the right side is known as the shift lever. This particular mechanism typically consists of 7 speeds that serve different functions during movement. To operate it, it is essential to match the appropriate derailleur and chainring in the following manner:

  • Disc number 1: used corresponding to gears number 1, number 2 and 3. Creates a light pedaling mode, the vehicle moves slowly in places with steep slopes. (should be used for mountain bikes, women’s sports bikes, men’s sports bikes)
  • Disc number 2: used corresponding to speeds number 3, 4, 5. Creates a normal pedaling mode.
  • Disc number 3: used corresponding to gears number 5, 6 and 7. Create a slow pedaling mode to gain momentum and accelerate the bike.
Read more: 5 Tips to Make Your Bike Faster

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3. How to adjust the starter

First and foremost, when adjusting a bicycle’s derailleur, particularly the rear derailleur, it is important to check the position of the control cable housing to ensure it adheres to regulations. This includes checking for any diagonal twists, as such irregularities could pose a safety hazard while riding.

In order to align the front starter, it is also important to carefully verify that the starter cable cover assembly is properly positioned and free from any twisting.

Start by rotating the starter handle to the left to position it on the smaller disc. Next, adjust the derailleur to the right to shift the rear derailleur to the highest gear. Lastly, turn the crank several times in one direction to ensure the bicycle chain aligns with the cassette.

After you have finished turning the crank, make sure to check if the chain lever and front derailleur chain are in contact with each other.

Afterwards, rotate the steering wheel to the left once more in order to transfer the previous segment onto the larger disc. Following that, adjust the right derailleur to shift the rear derailleur into the lowest gear. Then, rotate the crank a few times to verify if the chain and cassette are properly aligned.

After ensuring that the chain and cassette are properly matched, inspect if the chain comes into contact with the front derailleur lever. If there is contact, make adjustments to the H-shaped screw until the gap between the chain and a straight edge measures 2 mm. If you experience incomplete movement when shifting gears, examine and modify the tension of the derailleur cable.

4. Notes

4.1. Handle position

When using bicycle derailleurs, it is crucial to exercise caution. The right lever is intended for shifting the bike’s rear gears, whereas the left lever is for shifting the bike’s front fork.

4.2. Choose the right set of forks and cassettes

To ensure a comfortable and appropriate riding experience, it is essential to select forks and gears suited to your pedaling force and the terrain you plan to ride on. This way, you can enjoy a comfortable ride without exerting excessive effort.

Forks and traysForks and trays
Forks and trays

4.3. Shift Rules

Understanding the shifting rule is crucial as it helps in adapting your speed when transitioning from a level surface to a steep incline. Failing to comprehend these rules could pose a hazard while riding a bicycle.

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Before using the bicycle, it is essential to inspect all components, particularly the chain, as a crossed or misaligned chain can create difficulty and pose a hazard during use. Choosing the appropriate derailleur and sprocket settings is crucial to prevent such a scenario.

The gear lever is a fragile part that produces varying shifting forces. Therefore, it’s crucial to learn the rules of gear changing to achieve proper coordination between speeds and limits. Riding a bicycle in a chain-slipping condition can be hazardous.

By providing the article above, we aim to equip readers with valuable knowledge about bicycle derailleurs, along with essential tips for bicycle usage. We look forward to engaging with you through our next intriguing articles!

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Source: What is the role and importance of the derailleur on a bicycle?